Mixtures of organic fluids can be separated efficiently in an extractive distillation process. In such a process a selective solvent is utilized. This selective solvent is believed to change the solubility behavior of the two ingredients to be separated. Extractive distillation processes have been considerably improved in recent years. One such improved extractive distillation process is described in U.S. Pat. No. 4,053,369. Whereas it was believed for some time that in an extractive distillation process one should avoid the formation of two or more liquid phases it was discovered that the establishment of two liquid phases in certain situations aids the efficiency of an extractive distillation process. Therefore, it is described in the patent cited that the provision of two immiscible liquid phases in the upper portion of an extractive distillation column advantageously influences the separation efficiency of such an extraction distillation column and process.
The normal extractive distillation utilizes an extractive distillation column and a stripper. These two units may be combined into one but essentially maintain their function. The stripper serves to recover the solvent from the extract whereas the raffinate is recovered from the overhead effluent of the extractive distillation column.